This invention relates to a reciprocating-type fluid apparatus and, in particular, to a scroll-type fluid apparatus, such as a scroll compressor, for use in an air conditioner for a railroad car, an automobile, a house, and the like.
Referring to FIG. 1, an existing scroll compressor will be described. In the manner which will presently be described, the scroll compressor comprises a drive shaft or a crank shaft 1, a counterweight 2, an eccentric bush 3, a movable scroll member 4, and a fixed scroll member 5. The crank shaft 1 has an enlarged spindle portion 10 with a crank pin 110 eccentrically coupled thereto. The rotation of the crank shaft 1 on its own axis 99 (depicted by a dash-and-dot line in FIG. 1) causes the revolution of the crank pin 110 around the axis 99 of the crank shaft 1. The crank pin 110 is fitted into a crank pin receptacle 30 formed in the eccentric bush 3. The revolution of the crank pin 110 provides the revolution of the eccentric bush 3.
The movable scroll member 4 has a side plate 41, a spiral or involute lap 40 formed on one side of the side plate 41, and an annular boss 42 formed on the other side. The spiral or involute lap 40 will be called hereinafter a spiral element. The eccentric bush 3 is coupled to the boss 42 via a needle bearing 230 to be smoothly rotatable in the boss 42.
With the above-mentioned structure, the eccentric bush 3 and the movable scroll member 4 coupled thereto perform the revolution with respect to the crank shaft 1.
In order to suppress the rotation of the movable scroll member 4, a rotation inhibiting mechanism 210 is provided. The rotation inhibiting mechanism 210 comprises a pair of annular races 211 and a ball 212. By the rotation inhibiting mechanism 210, the movable scroll member 4 is allowed to perform the revolution alone.
Referring to FIG. 2 together with FIG. 1, the movable scroll member 4 has the spiral element 40 as described above. Likewise, the fixed scroll member 5 is provided a spiral element 50 having a shape similar to that of the spiral element 40. The movable scroll member 4 and the fixed scroll member 5 are arranged to be eccentric with each other by a predetermined distance with the spiral elements 40 and 50 shifted from each other by an angle of 180.degree.. With this structure, a plurality of closed spaces G are defined between the spiral elements 40 and 50 as illustrated in FIG. 2. An inner one and an outer one of the closed spaces G are smaller and greater in volume, respectively.
Therefore, a fluid sucked into the closed spaces G through a suction port (not shown) is transferred radially inward to be gradually compressed into a compressed fluid. Finally, the compressed fluid is led to a discharge port 6. The discharge port 6 is connected to a discharge chamber 8 through a discharge valve 7. The discharge chamber 8 is kept at a high pressure and the discharge valve 7 is normally closed under the high pressure in the discharge chamber 8. When the compressed fluid reaches the discharge port 6, the discharge valve 7 is opened under an increased pressure in the discharge port 6 so that the compressed fluid is discharged into the discharge chamber 8.
Thus, a series of operations mentioned above are carried out when the fluid is compressed by the scroll compressor. The components mentioned above are sealed in a casing 9 and a front housing 100 to be protected. A combination of the movable and the fixed scroll members 4 and 5 is referred to as a scroll-type transferring mechanism.
As illustrated in FIG. 1, the discharge valve 7 is attached to a base end wall 501 of the fixed scroll member 5 together with a retainer 80 by the use of a bolt 801 screwed into the base end wall 501 through the fixing hole 70.
Referring to FIGS. 3A through 3D, the structure of the discharge valve 7 will be described.
In FIG. 3A, the discharge valve 7 has a fixed portion 7a supported on the fixed scroll 5 and having a fixing hole 70, a closing portion 7b closing the discharge port 6, and a bridging portion 7c connecting the fixed portion 7a and the closing portion 7b. An outer contour of the discharge valve 7 is defined by a first arc 700a of the fixed portion 7a, a second arc 700b of the closing portion 7b, and a pair of straight lines 700c of the bridging portion 7c. The discharge valve 7 is a flap valve comprising an elastic plate. More particularly, the discharge valve 7 has a cantilevered structure having the fixed portion 7a fixedly supported on the fixed scroll member 5 and the closing portion 7b brought into contact with a peripheral edge of the discharge port 6 to close the discharge port 6.
The first arc 700a of the fixed portion 74 extends along a circle of a first diameter while the second arc 700b of the closing portion 7b extends along a circle of a second diameter. In the discharge valve 7 of FIG. 3A, the second diameter is determined greater than the first diameter. It will be understood that a diameter of the discharge port 6 is smaller than the second diameter. With this structure, the bridging portion 7c is widened from the fixed portion 7a towards the closing portion 7b. Contrary to the above-mentioned uniform strength beam, the bending stress is increased from the closing portion 7b towards the fixed portion 7a so that the discharge valve 7 is difficult to deflect. In addition, the stress is smaller towards the closing portion 7b, resulting in inefficiency.
The fixed portion 7a connected to a narrowest part of the bridging portion 7c may be subjected to stress concentration when the load is applied from the compressed fluid in the discharge port 6. Therefore, the life of the discharge valve 7 is inevitably shortened.
In FIG. 3B, the second diameter is determined smaller than the first diameter. With this structure, the bridging portion 7c connecting the fixed portion 7a and the closing portion 7b is gradually narrowed towards the closing portion 7b. However, the first arc 700a of the fixed portion 7a and the second arc 700b of the closing portion 7b are simply connected by the straight lines 700c of the bridging portion 7c. The diameter of the discharge port 6 must be smaller than the second diameter that is smaller than the first diameter.
In FIG. 3C, the second diameter is determined equal to the first diameter. In this case also, the valve-opening force is greater than that of the uniform strength beam mentioned above.
In FIG. 3D, the second diameter is determined greater than the first diameter, like in FIG. 3A. The first arc 700a of the fixed portion 7a and the second arc 700b of the closing portion 7b are connected by the parallel straight lines 700c of the bridging portion 7c. Even in this case, the valve-opening force is greater than that of the uniform strength beam mentioned above, like the structure illustrated in FIG. 3C. In addition, stress concentration may possibly occur at a portion depicted by a broken line in FIG. 3D between the first arc 700a and the straight lines 700c.
In each of the discharge valves of FIGS. 3A through 3D, the first arc 700a of the fixed portion 7a and the second arc 700b of the closing portion 7b are simply connected to each other by the straight lines 700c of the bridging portion 7c.
Referring to FIGS. 4A and 4B, description will be made about the technical background to discuss the rigidity problem.
At first, consideration will be made about a cantilevered beam comprising a rectangular plate illustrated in FIG. 4A. The rectangular plate will hereinafter be called a parallel beam.
The parallel beam has a rectangular section. The parallel beam has one end as a fixed end supported on a wall and the other end as a free end. The free end is subjected to a concentrated load.
The deflection y and the deflection angle i of the parallel beam are calculated as follows: ##EQU1##
where P represents a load, M, a bending moment, E, the Young's Modulus, and I, a moment of inertia of area.
In FIG. 4B, a cantilevered beam of a uniform strength beam has a rectangular section of a constant height h. The cantilevered beam will be called hereinafter a triangular beam. The triangular beam has one end as a fixed end supported on a wall and the other end as a free end subjected to a concentrated load.
The deflection y and the deflection angle i of the triangular beam are calculated as follows: ##EQU2##
where Z represents a section modulus.
As mentioned above, the height h of the section is constant. ##EQU3##
Comparison will be made between the deflections given by Equations (1) and (2) for the parallel beam and the triangular beam. EQU y.sub.max =y.sub.x=0 =Pl.sup.3 /3EI=4P/bE.multidot.(l/h).sup.3 (1) EQU y.sub.max =y.sub.x=0 =Pl.sup.3 /2EI.sub.0 =6P/b.sub.0 E.multidot.(l/h).sup.3 (2)
The ratio is calculated as follows: ##EQU4##
If b=b.sub.0, then y.sub.t =1.5y.sub.p. Thus, the deflection of the triangular beam is 1.5 times greater than that of the parallel beam. That is, the triangular beam is easily deflected.
Consideration will be made about the condition to obtain the relationship y.sub.t &gt;Y.sub.p.
y.sub.t -y.sub.p =(3b/2b.sub.0)y.sub.p -y.sub.p =3b-2b.sub.0 &gt;0 EQU .thrfore.1.5&gt;b.sub.0
If b=10, b.sub.0 &lt;15 mm.
Thus, if the value of b.sub.0 is selected within a range given by 1.5b&gt;b.sub.0, the deflection of the triangular beam is greater than that of the parallel beam.
As will be understood from the foregoing, the deflection of the parallel beam is smaller than that of the triangular beam, provided that the both beams have the constant height h, are subjected to the same load, and are equal in length to each other. Thus, the parallel beam is difficult to be deflected under the load and uses an unnecessarily large material as compared with the triangular beam. Specifically, according to the theory of the uniform strength beam, it is possible to provide a valve structure with the stress and the deflection in appropriate levels and to prolong the life of the valve. In the existing scroll compressor, the discharge valve has such a configuration that the first and the second arcs of the fixed portion and the closing portion are simply connected by the straight lines of the bridging portion.
Specifically, no consideration is made about the rigidity of the discharge valve in relation to the pressure of the fluid discharged through the discharge valve. The fixed portion and the closing portion are simply connected by the bridging portion configured to meet the shapes of he fixed portion and the closing portion. The deflection of the valve and the stress are not sufficiently considered. Therefore, the discharge valve has a high rigidity so that the valve-opening force is inevitably increased. This results in an increase in power consumption and a reduction in life of the valve.
From the above-mentioned formulas about the theory of the uniform strength beam, it is understood that the deflection of the parallel beam defined by parallel straight lines is smaller than that of the triangular beam defined by inclined straight lines and having the constant height h, provided that the both beams are subjected to the same load and are equal in length to each other. Therefore, the parallel beam is difficult to be deflected under the load and uses an unnecessarily large material as compared with the triangular beam. Specifically, according to the theory of the uniform strength beam, it is possible to provide a valve structure with the stress and the deflection in appropriate levels and to prolong the life of the valve.
With reference to FIGS. 5A and 5B, the operation of the discharge valve 7 will be described. At first referring to FIG. 5A, the scroll compressor performs low-speed rotation. In each cycle of the low-speed rotation, the discharge valve 7 is closed before discharge, opened during discharge, and closed after discharge as illustrated in the figure. Thus, the discharge valve 7 is repeatedly closed and opened.
Referring to FIG. 5B, the scroll compressor performs high-speed rotation. In this case, before the discharge valve 7 is closed at the end of a first cycle, discharge in a next cycle is started as illustrated in the figure. Therefore, the discharge valve 7 is not closed once the first cycle is started and repeatedly moved within a range depicted by dotted lines in FIG. 5B.
The discharge valve 7 is essential in order to avoid the backflow of the fluid although it is preferred in view of the efficiency of the compressor that the discharge valve 7 is not provided. The operation of the discharge valve 7 during the high speed rotation illustrated in FIG. 6B is preferable because the valve-opening force is reduced and the power consumption of the compressor is saved. Thus, the efficiency of the compressor is improved.
However, the existing discharge valve mentioned above is configured without considering mechanical properties and is difficult to be deflected because of a high rigidity. Therefore, the discharge valve is difficult to open. Thus, the compressor having the existing discharge valve is disadvantageous because the power consumption of the compressor is inevitably large.